This invention relates to a flow transducer, and more particularly to a device which can sense the flow of fluid and produce an electrical signal responsive thereto.
Flow transducers are typically utilized in various fluid systems to determine the rate of flow of the fluid. For example, in a system having fluid flowing within tubes or pipes, a flow transducer may be typically inserted into the flow stream so that the rate of flow can be continuously monitored. The output from the transducer is typically sent to a display device, which may include a meter or digital display, so that the actual rate of flow can be monitored or permanently recorded.
Frequently the flow transducer includes a rotating element which senses the flow of the fluid and produces a change in a characteristic which can be converted into an electrical signal, which is then measured. The electrical signal is then a function of the flow of the fluid.
Many problems have existed with prior art flow transducers because of their individual construction. For example, in many cases a rotor or other rotating device is utilized to detect the flow of the fluid and the rotor is supported by a housing. However, the spacing between the housing and the rotor is kept small in order to minimize the gap between the rotar's magnet and the housing's magnetic pickup. Such small spacing can frequently cause stalling of the rotor as the fluid, or impurities contained in the fluid, may jam the space causing the rotors to slow, stop or in many cases, even cause damage to the rotor.
Additionally, the various prior art transducers frequently utilize magnetic sensing whereby magnets are placed into the rotor in order to cause a change in a magnetic characteristic which can then be sensed. By placing the magnets directly in the rotor, the construction of the rotor becomes complex since it must be formed in sections and then assembled together with the magnets. Furthermore, it is difficult to vary the number of magnets since then the rotor would have to be redesigned to accommodate the different number of magnets. When placing the magnets in the rotor, the magnets may come in direct contact with the fluid. This can often damage the magnets, contaminate the fluid, and in some cases limit the use of the flow transducer. Frequently the magnet, when situated in the rotor, will accumulate ferrous particles on the exterior of the rotor and cause interference with the housing. Additionally, placing the magnets directly into the rotor increases the size and weight of the rotor, which thereby requires a heavier shaft to support the rotor. As a result, a greater flow of fluid is required to cause the rotor to move. Current flow sensors which utilize a magnet and sense a magnetic characteristic, do so through an inductance pickup utilizing a magnetic circuit including a magnetic core. This results in a magnetic stiction between the rotor and the housing through magnetic attraction between the pickup core and the rotor magnet. Therefore, many transducers cannot sense low flow rates and have inherent limitations to their use.